Patients with deep vein thrombosis of the lower extremities andor pelvis are eligible for this protocol if their thrombosis has been symptomatic for no more than 14 days and if their bleeding risk is very low. They are hospitalized for 3-7 days for up to 4 daily injections of rtPA directly into their thrombi. Simultaneously they receive anticoagulation, which is continued for 6 months. Since the last report we have enrolled 6 patients, for a total of 30. Extensive thrombolysis had been achieved with low doses of alteplase in every patient, and there have been no serious adverse events. The protocol is approved for 30 patients.